Physiology 3120 Lecture Notes - Lecture 2: White Blood Cell, Endothelium, Collecting Duct System
9 May 2018
School
Department
Course
Professor
Physiology 3120
Dr. Woods
Lecture 2
Barriers to Filtration
- we have barriers in the corpuscle
- there are things that can get into the space and other things that cannot
- things that should never be able to filter into the filtrate:
o proteins
o RBCs
o WBCs
- Why? Bc of the structure of the corpuscle
- The capillary is made of a single layer of endothelial cells that have holes in them (fenestrated)
- Components of the blood cannot go through endothelial cells, they can go in bw
- So the items that are small enough to go through the pores, can get through
- The podocyte is wrapped around the capillary
- The podocytes have spaces bw them called slits
- Items from the blood cannot go through the podocytes, but they can go thorugh the slits
- The podocytes (modified epithelial cells of bowmans capsule) are physically adhered to the
glomerular capillary bed
- The body adheres diff tissues together is through the use of an extracellular matrix called the
basal lamina
- STUDY GUIDE HAS A MISTAKE IN IT!!!
o Basal lamina and basement membrane are different
o They have a lot of things in common:
▪ Made of collagen type 4
▪ Have –ively charged glycoproteins
▪ Organized in layers
o Basal lamina lacks a layer which contains fibronectin (extracellular matrix component)
o If you have a layer that contains fibronectin, then it is called basement membrane
o But if it does not contain a layer with fibronectin in it, it is called basal lamina
- So the podocytes secrete basal lamina (lack fibronectin)
- Note: however, there is a basement membrane along the tubule – the epithelial cells sit along the
basement membrane, not a basal lamina
- So the basal lamina in the corpuscle is a collagen 4 matrix with –ively charged glycoproteins that
act like a sieve
o Type 4 collagen makes a mesh – allowing things to pass through it
- When things go through from the blood, they have to pass in bw the endothelial cells through
the pores, through the basal lamina, and through the slits of the podocytes to the lumen of the
bowmans capsule
- RBCs and WBCs are too big to be filtered (they are excluded by the pores – they are not large
enough)
- Proteins come in variable size (some are small, while others are large) but as a whole, proteins
have a –ive charge
- So proteins can either be excluded by the pore size (bc they are very large) or if the protein is
smaller, it can be excluded by the –ive charge of the basal lamina either way, proteins are not
filtered
- So the basal lamina provides an additional barrier for the proteins
- However, you will have some very small proteins (called peptides) that will make it through
- Also, podocytes are an extra protection to the slit sizes
- The main job of the podocytes is to restrict the fluid flow rate – the gaps within those podocytes
– if they are further apart, you can filter more fluid (and vice versa)
find more resources at oneclass.com
find more resources at oneclass.com
- Things that are able to filter into the filtrate:
o Water – the main solvent of plasma
o Ions – Na+, K+, Cl-, Ca2+ etc
o Amino acids
o glucose
Clinical Note: Urinalysis
- Overall health of the body can be quickly assessed by measuring components of urine.
- Test strips with colorimetric reactions have been developed to indicate substances in the urine.
- Leukocytes: BAD
o If you find leukocytes here, then there is a problem with the barriers to filtration
o Either the basal lamina is damaged or the pores for the glomerular capillaries have
become too wide bc WBCs are usually too big
- Nitrite: BAD
o Nitrates are GOOD
o Nitrites in urine means you have a bacterial infection bc bacteria will metabolize
nitrate and turn it into nitrite
- Urobilinogen: GOOD at low concentrations and BAD at high concentrations
o There is always going to be low concentrations of urobilinogen
o Hb gets broken down into a number of diff metabolites to bilirubin which gets
broken down into urobilinogen
o If you find high levels, its due to a blockage in your bile duct
o Too much urobilinogen means that the liver is unable to do its job or its blocked
- Proteins: BAD
o Bc its usually too big and should never make it into urine
o Means there is a problem with the barrier to filtration
o Pregnant women might show this (body adapting to pregnancy can have changes
to kidney)
o Sometimes, if we eat too much protein, we will have protein in urine
- pH: 6 is normal
o slightly acidic bc most of the foods we each is acidic so the body will compensate
by excreting some of that acid
- Haemoglobin: BAD
o )t’s a protein normally found in your RBCs
o Hb should not make it out into the plasma
o If Hb is in the blood plasma, that means hemolysis happens (RBCs destruction for
whatever reason – disease, drugs, anemia etc)
- Specific gravity: too high is BAD
find more resources at oneclass.com
find more resources at oneclass.com
Document Summary
We have barriers in the corpuscle there are things that can get into the space and other things that cannot things that should never be able to filter into the filtrate: proteins, rbcs, wbcs. So the items that are small enough to go through the pores, can get through. The capillary is made of a single layer of endothelial cells that have holes in them (fenestrated) Components of the blood cannot go through endothelial cells, they can go in bw. The podocyte is wrapped around the capillary. The podocytes have spaces bw them called slits. The podocytes (modified epithelial cells of bowmans capsule) are physically adhered to the. Items from the blood cannot go through the podocytes, but they can go thorugh the slits glomerular capillary bed. The body adheres diff tissues together is through the use of an extracellular matrix called the basal lamina.
